Instancing texture mapping not working?
This is actually a known issue with From Instancer option (see here for more on that). Good news is that it's just a viewport bug, it renders just fine.

Quick tip as well since you'll have to render the image to see any updates: If you use emission shaders only you can render noise free with 1 sample in Cycles and it's super quick. Won't help with diffuse/glossy/glass etc., but for just previewing colors it may help.